fix: keep NIP-29 group reactions in the group so likes notify

A "like" on a group message was built as a plain NIP-25 reaction — `e`
(message) + `p` (author) + `k` — with no `h` tag. The recipient's only
notification query that reaches the group's host relay,
filterGroupNotificationsToPubkey, is scoped `#p`=them AND `#h`=their
groups (kind 7 is already in GroupNotificationKinds), so a like with no
`h` tag is never matched there. It would only surface if NIP-65 routing
happened to drop it on one of the recipient's inbox relays — never for a
host-relay-only group — so likes on group messages effectively never
notified.

Copy the target's `h` tag onto public reactions to group-scoped events,
mirroring how kind-9 replies carry it. ReactionEvent.build gains an
`initializer` (the API GroupScope's KDoc already documented); ReactionAction
applies the group `h` tag for both the tracked and fire-and-forget paths.
The like now lands on the host relay in-group and the existing kind-7
`#p`+`#h` query picks it up.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VxpT7J4xt37EF5yJDw1htK

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/nip25Reactions/ReactionAction.kt

@@ -24,12 +24,16 @@ import com.vitorpamplona.amethyst.commons.model.Note
 import com.vitorpamplona.amethyst.commons.model.User
 import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 import com.vitorpamplona.quartz.nip01Core.hints.EventHintBundle
+import com.vitorpamplona.quartz.nip01Core.signers.EventTemplate
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
 import com.vitorpamplona.quartz.nip01Core.tags.people.taggedUserIds
 import com.vitorpamplona.quartz.nip17Dm.NIP17Factory
 import com.vitorpamplona.quartz.nip17Dm.base.NIP17Group
 import com.vitorpamplona.quartz.nip25Reactions.ReactionEvent
+import com.vitorpamplona.quartz.nip29RelayGroups.groupId
+import com.vitorpamplona.quartz.nip29RelayGroups.hTag
 import com.vitorpamplona.quartz.nip30CustomEmoji.EmojiUrlTag
 
 /**
@@ -64,21 +68,39 @@ object ReactionAction {
             throw IllegalStateException("Cannot react publicly to a private rumor")
         }
 
-        // Handle custom emoji reactions (format: ":emoji_name:")
-        val template =
-            if (reaction.startsWith(":")) {
-                val emojiUrl = EmojiUrlTag.decode(reaction)
-                if (emojiUrl != null) {
-                    ReactionEvent.build(emojiUrl, eventHint)
-                } else {
-                    // Fallback to text if emoji decode fails
-                    ReactionEvent.build(reaction, eventHint)
-                }
-            } else {
-                ReactionEvent.build(reaction, eventHint)
-            }
+        return signer.sign(buildPublicReaction(eventHint, reaction))
+    }
 
-        return signer.sign(template)
+    /**
+     * Builds a public reaction template for [eventHint], decoding a custom-emoji
+     * reaction when present and falling back to plain text otherwise.
+     *
+     * When the target is a NIP-29 group event (it carries an `h` tag), the
+     * reaction copies that `h` tag so the like stays scoped to the group and
+     * lands on the group's host relay — where the recipient's group-notification
+     * subscription (`#p`=them + `#h`=their groups, kind 7 included) can match it.
+     * Without the `h` tag the like is a plain kind-7 that the host-relay query
+     * never sees, so a reaction to someone's group message would only reach them
+     * on the off chance NIP-65 routing delivered it to one of their inbox relays
+     * — never for a host-relay-only group. This mirrors how kind-9 replies carry
+     * the `h` tag to be notifiable.
+     */
+    private fun buildPublicReaction(
+        eventHint: EventHintBundle<Event>,
+        reaction: String,
+    ): EventTemplate<ReactionEvent> {
+        val groupScope: TagArrayBuilder<ReactionEvent>.() -> Unit = {
+            eventHint.event.groupId()?.let { hTag(it) }
+        }
+
+        if (reaction.startsWith(":")) {
+            val emojiUrl = EmojiUrlTag.decode(reaction)
+            if (emojiUrl != null) {
+                return ReactionEvent.build(emojiUrl, eventHint, initializer = groupScope)
+            }
+            // Fallback to text if emoji decode fails
+        }
+        return ReactionEvent.build(reaction, eventHint, initializer = groupScope)
     }
 
     /**
@@ -159,19 +181,7 @@ object ReactionAction {
             )
         } else {
             // Public reaction
-            val template =
-                if (reaction.startsWith(":")) {
-                    val emojiUrl = EmojiUrlTag.decode(reaction)
-                    if (emojiUrl != null) {
-                        ReactionEvent.build(emojiUrl, eventHint)
-                    } else {
-                        ReactionEvent.build(reaction, eventHint)
-                    }
-                } else {
-                    ReactionEvent.build(reaction, eventHint)
-                }
-
-            onPublic(signer.sign(template))
+            onPublic(signer.sign(buildPublicReaction(eventHint, reaction)))
         }
     }
 

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/model/nip25Reactions/ReactionActionTest.kt

@@ -27,9 +27,12 @@ import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
 import com.vitorpamplona.quartz.nip01Core.tags.people.PTag
 import com.vitorpamplona.quartz.nip01Core.tags.people.pTags
 import com.vitorpamplona.quartz.nip10Notes.TextNoteEvent
+import com.vitorpamplona.quartz.nip29RelayGroups.hTag
+import com.vitorpamplona.quartz.nipC7Chats.ChatEvent
 import kotlinx.coroutines.test.runTest
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 import kotlin.test.fail
 
@@ -57,12 +60,46 @@ class ReactionActionTest {
                     publicCalls++
                     assertTrue(reaction.sig.isNotEmpty(), "public reaction must be signed")
                     assertTrue(reaction.tags.any { it.size >= 2 && it[0] == "e" && it[1] == note.id })
+                    assertFalse(
+                        reaction.tags.any { it.isNotEmpty() && it[0] == "h" },
+                        "a reaction to a non-group note must not carry an `h` tag",
+                    )
                 },
                 onPrivate = { fail("reaction to a public note must not be gift-wrapped") },
             )
             assertEquals(1, publicCalls)
         }
 
+    @Test
+    fun reactionToRelayGroupMessage_carriesTheGroupHTag() =
+        runTest {
+            // A NIP-29 group chat message: a kind-9 ChatEvent scoped by `h`.
+            val groupId = "abcd1234"
+            val groupMessage = aliceSigner.sign(ChatEvent.build("gm") { hTag(groupId) })
+
+            var publicCalls = 0
+            ReactionAction.reactToWithGroupSupport(
+                eventHint = EventHintBundle(groupMessage, null),
+                reaction = "+",
+                signer = bobSigner,
+                onPublic = { reaction ->
+                    publicCalls++
+                    // Standard NIP-25 targeting …
+                    assertTrue(reaction.tags.any { it.size >= 2 && it[0] == "e" && it[1] == groupMessage.id })
+                    assertTrue(reaction.tags.any { it.size >= 2 && it[0] == "p" && it[1] == aliceSigner.pubKey })
+                    // … plus the group `h` tag copied from the target, so the like
+                    // stays in the group and the recipient's `#p`+`#h` host-relay
+                    // notification query can match it.
+                    assertTrue(
+                        reaction.tags.any { it.size >= 2 && it[0] == "h" && it[1] == groupId },
+                        "a reaction to a NIP-29 group message must copy the group's `h` tag",
+                    )
+                },
+                onPrivate = { fail("a public group message reaction must not be gift-wrapped") },
+            )
+            assertEquals(1, publicCalls)
+        }
+
     @Test
     fun reactionToUnsealedRumor_isGiftWrappedToAllParticipants() =
         runTest {

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip25Reactions/ReactionEvent.kt

@@ -24,6 +24,7 @@ import androidx.compose.runtime.Immutable
 import com.vitorpamplona.quartz.nip01Core.core.AddressableEvent
 import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 import com.vitorpamplona.quartz.nip01Core.hints.AddressHintProvider
 import com.vitorpamplona.quartz.nip01Core.hints.EventHintBundle
 import com.vitorpamplona.quartz.nip01Core.hints.EventHintProvider
@@ -88,6 +89,7 @@ class ReactionEvent(
             reaction: String,
             reactedTo: EventHintBundle<Event>,
             createdAt: Long = TimeUtils.now(),
+            initializer: TagArrayBuilder<ReactionEvent>.() -> Unit = {},
         ) = eventTemplate<ReactionEvent>(KIND, reaction, createdAt) {
             eTag(reactedTo.toETag())
             if (reactedTo.event is AddressableEvent) {
@@ -95,12 +97,14 @@ class ReactionEvent(
             }
             pTag(reactedTo.event.pubKey, reactedTo.relay)
             kind(reactedTo.event.kind)
+            initializer()
         }
 
         fun build(
             reaction: EmojiUrlTag,
             reactedTo: EventHintBundle<Event>,
             createdAt: Long = TimeUtils.now(),
+            initializer: TagArrayBuilder<ReactionEvent>.() -> Unit = {},
         ) = eventTemplate<ReactionEvent>(KIND, reaction.toContentEncode(), createdAt) {
             eTag(reactedTo.toETag())
             if (reactedTo.event is AddressableEvent) {
@@ -109,6 +113,7 @@ class ReactionEvent(
             pTag(reactedTo.event.pubKey, reactedTo.relay)
             kind(reactedTo.event.kind)
             emoji(reaction)
+            initializer()
         }
     }
 }